A sex pillow is a soft implement used to enhance sexual intercourse

Sexual intercourse

Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...

. An ordinary (typically firm, since soft pillows have a shock absorbing effect) pillow can be used. But there are also specially-designed sex pillows. Some even have a high-density urethane

Polyurethane

A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...

 core to balance firm support with softness. In addition to more common pillow shapes, there are wedge-shaped, ramp-shaped, prism-shaped, etc. pillows which lend themselves to various sexual positions, some of which might be difficult or uncomfortable without it. A pillow can be used to provide support when one partner has back pain. A very common use of a sex pillow is to place it under the woman's buttocks or hips before assuming the missionary position

Missionary position

The missionary position is a "man-on-top" sex position usually described as the act in which the woman lies on her back and the partners face each other. Though often acted on and applied by heterosexual pairings, it may also be used by gay and lesbian couples.The missionary position is an example...

; this pivots the pelvis and increases depth of penetration. Invented by Louis Friedman and Don Cohen in 2001, Liberator shapes

Liberator shapes

Liberator Shapes are adult pillows used for sexual positioning. Founded in 2001, Liberator Inc., also known as OneUp Innovations, operates out of their factory in Atlanta, GA...

were the first patented pillows designed specifically for sex